1. Field of the Invention
This invention pertains to the manufacture of sterile or disinfected articles by three-dimensional printing.
2. Description of the Related Art
Manufacturing of medical articles must be done in conditions that are, depending on the needs of a particular article, clean, aseptic, sterile, or what is described in regulations as being under conditions of Good Manufacturing Practice. Sterility represents the highest degree of killing of microorganisms, and disinfection represents a somewhat lesser degree. Commonly used methods for killing or damaging microorganisms have included gamma radiation, electron beam radiation and other forms of ionizing radiation, and have also included heat and harsh chemicals in gaseous or liquid or other form.
Another technique that has been used for killing or damaging microorganisms, although it has been considered less aggressive than the above techniques, has been exposure to ultraviolet light. Ultraviolet light is more energetic than visible light. Proteins and nucleic acid, which all microorganisms contain, absorb light and can thereby suffer damage that kills the microorganisms or prevents their reproduction. In some instances several of these techniques have been applied to manufactured articles at the last stage of a manufacturing operation (terminal sterilization). In some instances several of these techniques have, additionally or instead, been applied either to materials or to equipment either before manufacturing or during or between any of various stages of manufacturing.
Three-dimensional printing (3DP) has had industrial and commercial applications including both rapid prototyping and fabrication of actual products. Three-dimensional printing described in U.S. Pat. No. 5,204,055 and elsewhere, is the manufacture of objects by assembling them from powder in a layer-by-layer fashion. It is illustrated in FIG. 1. In this process, layers of powder have been deposited by roller spreading or by other means. When the powder deposition has been by roller spreading, powder has been presented by raising a feed bed, and has been pushed by a roller from the feed bed to a build bed, where it has been spread in a thin layer. In selected places in the build bed, powder particles have then been joined to other powder particles and to other bound regions by the action of a binder liquid that has been dispensed from a dispenser such as a dispenser resembling an ink-jet printer. Binding has occurred as a result of a non-volatile substance being deposited by the binder fluid or dissolved by the binder fluid as the binder fluid lands on the powder bed, or has occurred as a result of dissolution of powder particles followed by re-solidification. Unbound powder has supported bound regions during printing and has later been removed after completion of 3DP.
In the medical field, 3DP is beginning to be used for direct manufacturing of some medical articles. Direct manufacturing of medical articles by 3DP can be more demanding than direct manufacturing of general industrial and commercial articles, at least because of the need for appropriate levels of cleanliness. Until now, traditional aseptic manufacturing techniques have not been adapted to three-dimensional printing, except to the extent described in the co-pending commonly assigned patent application referenced herein, which is incorporated by reference. More specifically, the use of ultraviolet light has not been applied to the process or apparatus of three-dimensional printing for purposes of sterilization or disinfection, although ultraviolet light has been employed for the purpose of chemically curing or cross-linking a binder substance such as in U.S. Pat. Nos. 6,467,897 and 6,696,073.
In addition to the general difficulty of implementing aseptic techniques on a piece of machinery having the complexity of a 3DP machine, there is also the issue that some articles manufactured for medical applications may contain fragile organic substances such as Active Pharmaceuticals Ingredients, growth factors, and even cells, any of which may be important in determining the performance of the medical article when it interacts with a living body. Such substances may be decomposed or damaged by many of the traditional sterilization techniques such as ionizing radiation, heat, and harsh chemicals. It is less likely, although still possible, that such substances may be decomposed or damaged by exposure to ultraviolet light. For example, it is known that microorganisms that contaminate blood are destroyed by ultraviolet light while the blood platelets, blood plasma and red blood cells are not damaged.
Accordingly, it would be desirable to provide ways of disinfecting or sterilizing machine apparatus used in three-dimensional printing. It would also be desirable to provide ways of sterilizing or disinfecting powder as the powder is in the three-dimensional printing machine. This might be desirable either when the powder is in a stationary situation or when the powder is in a situation where it is being moved. It would be desirable to achieve the desired degree of killing or damaging of microorganisms as much as possible relatively early in a manufacturing process, prior to the possible introduction of fragile substances into the article, and perhaps thereby avoid the need for terminal sterilization, which might damage the fragile substances. It would be desirable to accomplish the sterilization or disinfection using, at least partially, ultraviolet light. It would be desirable to have a sterilization or disinfection method which is well adapted to manufacturing an article in a layer-by-layer fashion so that the method can sterilize the material of each layer around the time of the manufacturing processes which affect that particular layer.